In manufacturing a semiconductor device, a cleaning system is employed in order to perform a cleaning before diffusion/CVD processing, a cleaning after etching, and a wet etching. The cleaning system has been highly integrated in recent years in order to meet requirements for a small footprint and a high throughput, such that a plurality of cleaning units are included in one cleaning processing system.
Although an exclusive cleaning liquid supply unit may be installed in each of the cleaning units, a common cleaning liquid supply unit is generally installed with respect to the plurality of cleaning units. A cleaning liquid is generally generated by mixing one kind or a plurality of kinds of highly concentrated chemical solutions with deionized water (DIW). While the cleaning liquid is generated in advance to be stored in a tank, the cleaning liquid may be supplied from the tank as necessary. However, in recent years, the chemical solutions-DIW mixing has been performed at the time of supplying a processing liquid. The plurality of cleaning units is operated according to a predetermined process schedule, and the number of cleaning units using the cleaning liquid varies every moment. There may be a case either only one cleaning unit uses the cleaning liquid, or all cleaning units use the cleaning liquid. In particular, since the chemical solution is highly corrosive, a flow rate control apparatus in which at least a liquid contacting portion is made of a chemical-resistant resin material needs to be used and a flow rate regulation range thereof is generally very narrow. Accordingly, if the number of cleaning units included in one cleaning processing system increases, the flow rate control apparatus for the chemical solution with the narrow flow regulating range has difficulty in dealing with the variations of a flow rate of the required chemical solution.
According to user's requirements, one cleaning liquid supply unit may be required to supply a relatively low-concentration cleaning liquid (for example, DHF of HF:DIW=1:200) and a relatively high-concentration cleaning liquid (for example, DHF of HF:DIW=1:10). Further, one cleaning liquid supply unit may be required to supply different types of cleaning liquids (for example, DHF, SC1, and SC2). In this case, the flow rate control apparatus for the chemical solution with the narrow flow regulating range becomes more difficult to deal with variations of the flow rate of the required chemical solution. As an example, the flow rate control apparatus for the chemical solution may have to deal with a wide range in the flow rate of the chemical solution in the range of approximately 10 ml/min to 2800 ml/min.
Japanese Patent Application Laid-Open Publication No. 2003-158122 discloses a technique in which two flow rate controllers having different controllable flow rate ranges and installed in parallel are used in order to supply a liquid raw material in a CVD device. However, Japanese Patent Application Laid-Open Publication No. 2003-158122 does not at all disclose controlling of two flow rate controllers which can deal with the variations in the required flow rate.